In most household tumble dryers, if an automatic cycles is selected, an algorithm chooses the cycle duration based on the signal coming from a sensor measuring a certain parameter, for instance clothes conductivity (by means for instance of metal strips) or air humidity. In other words, the signal coming from the sensor is directly correlated to the moisture content of the clothes, whose value is compared with a threshold to detect the end of the drying cycle.
Unfortunately, this known approach may suffer from several problems. For example, if clothes conductivity parameter is used, the values thereof based on signals coming from the conductivity strips are highly correlated to the water hardness, which may vary from region to region. Moreover, the conductivity value is related to the fabric type and, in case of a synthetic load, a static electricity phenomena (that often appear during the end of the cycle) may interfere with the sensor information.
Further still, the conductivity strips may provide an unreliable signal in case of small loads or in case of bulky items, because the strips simply measure the moisture of the load surface. Similarly, the information coming from air humidity sensor is affected by the accumulation of lint on the sensor surface, which may lead to inaccuracy of measurement due to its position and by occurrence of condensation on the sensor surface.
Methods for automatically detecting end of drying cycle by means of temperature information are also known. Unfortunately, these methods are affected by inaccuracy when customer desires a termination of the cycle with a relatively high remaining moisture content (e.g. to make ironing easier).
For all the above reasons, the performances of end of cycle information coming from a single sensor (e.g., a temperature sensor, a conductivity sensor or a humidity sensor) may lead to under-drying or over-drying of the clothes that respectively means unsatisfied customers, or wasted energy and time together with possible fabric damage.